Book Chapter 14-Home

Hunting Bullet Metrics

Apply Terminal Performance Truth

AFRICA HUNTER QUEST©

Chapter 14 - THE SOLID COPPER BULLET

GG: Based on what you learned about cup and core bullets, what general bullet performance extreme do you think can be assigned to it?

D: At high impact velocities, potentially heavy emphasis on wound cavity volume at the expense of penetration.

GG: Excellent. If that is the case, what general bullet performance extreme do you think is opposite?

D: Potentially heavy emphasis on penetration at the expense of wound cavity volume.

GG: Exactly. The generic bullet typically associated with strong penetration is one made from solid copper.

D: Solid copper? A cup and core bullet without the lead?

GG: No. The jacket material for a cup and core bullet is a copper alloy. The metallurgy of the alloy is designed to allow easy forming of the jacket around the lead core. This alloy is way softer than solid copper.

Through manufacturing wizardry, the finished solid copper bullet has a small diameter hole of limited depth at the tip to initiate expansion. Some solid copper bullets have a poly tip embedded in the tip to also help initiate expansion. The surface of the hole in the tip’s interior is scored with limited-depth incisions in the hole’s periphery, typically oriented 90 degrees apart. These incisions weaken the bullet’s tip to allow it to blossom upon impact into four equal petals of copper. These petals typically create a symmetric mushroom shape. The extent of the mushroom diameter can be controlled somewhat by the depth of the hole in the tip, but I think more by the depth and length of the incisions in the nose. The tip can be annealed (softened) to various degrees to either enhance or retard the rate and the extent to which the tip expansion occurs.

Before we go any further, I want to emphasize these solid copper bullets expand. The modifying word ‘solid’ should not be confused with an actual generic

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bullet design that is called just ‘solids’. ‘Solids’ are used primarily to hunt very large dangerous game, like elephant. They’re designed not to expand. Not only that, the best ones are designed not to even deform. So, when I use the term ‘solid copper bullet’, it means the bullet is constructed entirely of copper, no other metal.

The specific gravity of lead is about 28% greater than the specific gravity of copper. That means in order for a solid copper bullet to weigh the same as a conventional lead core bullet, its volume has to be 28% greater. The net result is that solid copper bullets are longer than an equal weight lead core bullet, and this length can result in reducing the powder charge in the cases with some chamberings.

The relatively long shanks of solid copper bullets can increase drag in the barrel as well as increase fouling. Most of these bullets have peripheral, reduced diameter grooves of some sort machined into the shank as compensation to reduce drag.

I did gel testing on four bullets of this generic design. Three were 35-caliber and one was 30-caliber. All were flat-base spitzers from the same manufacturer. The 35-caliber bullets were fired from my 358 Winchester, and the 30-caliber was fired from a friend’s 308 Winchester.

I had only planned to do testing on one, 35-caliber, 225-grain bullet. However, this stock bullet, one with no factory-installed poly tip, failed to expand at an impact velocity of 2219 fps and completely penetrated through the third gel block. As far as I was concerned, this bullet failed to perform satisfactorily and was relegated to last place in the competition.

In the engineering world, the best lessons learned are from analyzing failure, trying to figure out the whys and the hows. The 225-solid copper bullet ‘failure’ was actually a blessing in disguise because it forced me to focus on bullet terminal performance concepts that I may not have discovered otherwise.

To be useful as a hunting bullet out of my 358 Winchester, the 225-grainer needed to expand so that a credible wound cavity was formed. My first attempt to get this bullet to expand was to hand-install what I am calling a ‘small’ poly tip. To both install this tip and weaken the copper at the nose of the bullet, I drilled a hole 0.090 inches in diameter, 0.575 inches deep into the bullet. At an impact velocity of 2283 fps, this bullet penetrated 36½ inches into the gel. The recovered bullet had a weight retained of 99%, a deformation of 22%, and an expansion ratio of

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1.68. The retained bullet had blossomed into four petals forming a mushroom that was almost perfectly round. There was no apparent tumbling by the bullet. The wound cavity looked like an anemic eel-snake.

As I have already told you, I am a proponent of terminal bullet performance balanced between wound cavity volume and penetration. As far as I was concerned, the cavity formed by this modified bullet with a ‘small’ tip was marginal, bordering on unacceptable.

I had a larger tip available. This ‘large’ tip required drilling a larger, 0.115-inch diameter hole for installation. I reasoned the bullet’s tip would be further weakened by this larger diameter hole, thus causing more rapid initial expansion to form the mushroom. I further postulated that this more rapid rate of mushroom formation would cause both a larger wound cavity volume and a larger maximum diameter of the cavity, but at the expense of less total penetration.

This 225-grainer with the ‘large’ poly tip had an impact velocity of 2297 fps and penetrated 33-3/4 inches. The recovered bullet had a weight retained of 99%, a deformation of 22%, and an expansion ratio of 1.60. Again, the retained bullet had a four-petal mushroom that was almost perfectly round and there was no apparent evidence that the bullet had tumbled. The wound cavity looked like an anemic guppy, trying to morph into an eel-snake.

The test results obtained with the large poly tip demonstrated that all of my wound cavity postulations had been achieved. The wound cavity created by using the large poly tip was about 9% greater than the one created with using the small poly tip, and the maximum diameter of the cavity was about 4% greater. As expected, the total penetration length obtained by using the large-tip bullet was about 2¾ inches less. The more rapid development of the cavity it had caused also increased what I believe is the potential to induce hydrodynamic shock by a factor of at least 2.

Donny sat there in silence, processing the Geezer’s input. The output was bull$#!+. “This is bogus mad science,” thought Donny. “Nobody can correctly postulate all that cause and effect from seeing just one supposedly good test result. I knew damn-well numbers were being tortured to justify the old coot’s mental masturbation”.

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GG eyed the Pilgrim, the vibe almost palpable. Undeterred, he pressed on, piling it on. “Time to see if the youngun can be force fed a heavy dose of reality,” thought GG.

GG: The diameter and depth of both holes I drilled in order to install the poly tips could be described as major structural carnage, a premeditated attempt to weaken the tip area. I was concerned I was removing so much metal from the tip that I would shear off big copper chunks of nose, particularly from installing the ‘large’ tip. Not so. Both tipped 35-caliber bullets produced nearly symmetrical mushrooms with nearly the same expansion ratio. What was even more remarkable was that the total recovered bullet length due to longitudinal deformation was nearly identical. Even with a larger diameter hole, the bullet with the ‘large’ tip had essentially deformed to the same length as the bullet with the ‘small’ tip.

I think it’s important to point out several general comparisons with the cup and core bullets that help explain the gel test results of these solid copper bullets. First, the length-wise deformation of the solid copper bullets was about half of the typical deformations of the cup and cores. Theoretical physics says that bullets with lower length-wise deformation should penetrate more. That was the case, as these butchered, 35-caliber, solid copper bullets out penetrated the cup and cores by factors that ranged from 1.09 to 1.85 times. What also likely contributed to this increased penetration was that these 35-caliber solid copper bullets had symmetric, virtually round mushrooms that reduced the potential for tumbling. Also, the expansion ratios of the solid copper bullets were significantly less, with values less than 1.7, compared to the expansion ratios for the cup and cores which were at least 1.83 and ranged up to 2.17. Finally, the tougher copper of the solid copper tips likely caused these bullets to expand slower, thus contributing to enhanced penetration.

Even though these 225-grain, 35-caliber solid copper bullets significantly out penetrated all cup and cores, the wound cavity volumes produced could be considered comparatively anemic. These tipped 35-caliber solid copper bullets out penetrated the 225-grain cup and core bullet by a factor of about 1.8, but the total wound cavity volume for the 225-grain cup and core was pretty much the same as the ‘large’ tip solid copper bullet. Even though both of the tipped, 35-caliber 225-grain solid copper bullets out penetrated the 35-caliber, 250-grain cup and core bullet by factors ranging from 1.06 to 1.14, the 250-grainer had a wound cavity volume about 1.36 times greater than the ‘large’ tip, 225 solid copper bullet.

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The test results for the 30-caliber, 165-grain solid copper bullet with no poly tip virtually mirrored the results of the 35-calibers with poly tips. The impact velocity of the 165-grainer was 2350 fps, a good 130 fps faster than the 35-caliber, tipped 225-grainers. Yet the penetration was comparable at 34-3/4 inches, the retained weigh comparable at 100%, the deformation comparable at 23%, and the expansion ratio comparable at 1.69. Like the tipped 35-calibers, the recovered 165-grainer had an almost perfectly round, four-petal mushroom and showed no apparent indication that it had tumbled.

The wound cavity produced by the 165-grainer looked like a really pathetic eel-snake, actually looking like it wanted to morph into just a snake. Its wound cavity volume was, by far, the lowest of all the bullets tested, regardless of its excellent penetration. Its nearest wound cavity volume rival, the 30-caliber, 220-grain cup and core, had a total wound cavity volume 1.57 times greater with a penetration length of only 19 inches, about 55% of the 165-grainer’s penetration. The 30-caliber, tipped 240-grain cup and core match bullet had a cavity volume 1.61 times greater with a penetration length of only 20-1/2 inches, about 59% of the 165-grainer’s penetration.

What stunned me was the commonality of deformation, expansion ratio, and penetration length of the untipped 165-grainer compared to the tipped, 35-calibers considering the butcher job I had done to install the tips. Coincidence? Could be, but I think not.

Because these solid copper bullets were all from the same manufacturer, I concluded that the gel test results indicated a premeditated terminal performance objective focused on penetration. As a consequence, wound cavity volume was relatively modest, particularly compared to that produced by the cup and cores of the same caliber. The anemic, almost snake-like cavity produced by the stock, unaltered 165-grainer certainly indicated penetration was favored over wound cavity formation.

Donny sat there numb. What he had just been told was so outlandish that it fell into the category of “Ya can’t make this $#!+ up”. Therefore, it had to be true. “Damn him,” thought Donny.

Donny re-engaged his brain that had remained in free-wheel mode ever since the Old Man began describing the precision by which he had mangled perfectly good bullets.

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D: So, what do you think are the design features of this particular generic bullet that would help achieve a premeditated objective of penetration?

GG: I’ve already touched on them when I was comparing these solid copper bullet results to those of the cup and cores. But this would be a good spot to knit everything up.

I think there are four conceptual ways. The first is to limit deformation in terms of bullet length and mushroom diameter. Theoretical physics says an object will penetrate more if its deformation is reduced along its length. That is the basis for designing crush zones at both the front and rear of cars. In that instance, designers want more deformation to limit impact forces and penetration of a vehicle into a barrier. All these solid copper bullets deformed an average of 21% of their length. In contrast, the cup and core bullets I tested deformed from 44 to 59%, from about double to almost triple the deformations of these solid copper bullets. The limited longitudinal deformation exhibited by these solid copper bullets was likely a contributing factor for this generic design having an average penetration length about 1.5 times greater than the average penetration length of all the cup and cores tested.

Even with structurally obscene holes drilled into them, the copper was thick enough and strong enough at the base of the petals that were formed to prevent further deformation, in this case further blossoming of the petals to form a larger diameter mushroom shape. The commonality of the expansion ratios also suggests the depth and length of internal scoring in the nose area, coupled with potential strategic annealing of the bullet’s nose, are premeditated design and manufacturing efforts to limit the extent of the mushroom’s formation in both its length and diameter.

That brings us to the second component of deformation: the actual radial limits to which these mushrooms deformed. The expansion ratio of these solid copper bullets averaged about 1.65. In contrast, the expansion ratio of the cup and core bullets ranged from 1.83 to 2.17, with an average of 1.92. This average is about 16% more than the average solid copper bullets’ expansion ratios. Smaller diameter mushrooms have less drag, so they penetrate more. Again, based on the commonality of these solid copper bullets’ expansion ratios and the fact that all of these solid copper bullets lost a maximum of about 1% of their weight, I believe the mushroom diameter of the retained bullets is the maximum that was produced during penetration.

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Third, the rate at which the mushroom deformed influences the penetration length. The copper used to construct these bullets is obviously way stronger than lead, and thus more resistant to deformation that causes the mushroom to form. The stronger material takes longer to deform, causing the mushroom to form way slower than if the material had been lead. The slower blossoming of the mushroom allows the bullet to penetrate further before full expansion occurs.

Finally, the strength of the copper and the precision installation of the four incisions in the nose causes the mushroom formed by these bullets to be almost perfectly round. That symmetry facilitates straight-arrow plowing with limited potential for trajectory deviations or tumbling. In contrast, there are no design features in a simple cup and core bullet to limit, regulate, and maintain mushroom symmetry. Compared to solid copper bullets, this expansion can be characterized as rapid and helter-skelter, oftentimes resulting in an egg-shaped mushroom that can even be off axis to the bullet. These egg-shaped and off-axis mushrooms can cause both trajectory deviations and tumbling.

All of the cup and core bullets had egg-shaped mushrooms to varying degrees. Only the .375-caliber, 300-grainer had a mushroom with a maximum and minimum diameter indicating it was almost round. That bullet was assessed not to tumble. The remaining four cup and cores all had visually obvious, egg-shaped mushrooms. These remaining four showed evidence of tumbling or beginning to tumble near their termination limit.

There may be other design and manufacturing techniques to control deformation in these solid copper bullets besides internally scoring a cavity inside the bullet’s nose and strategic annealing. No one has offered the ‘secret handshake’ to explain what they are.

D: All of the bullet mangling you did to the 35-caliber, 225-grainer was an effort to get it to expand. How do you know the stock bullet didn’t expand if you didn’t retain one in the third gel block?

GG: Very astute observation. Two reasons: the cavity I got in all the blocks looked like a snake, not trying to become one. The second reason is I managed to capture a stock 225-grainer in my very first test that didn’t turn out so hot. Bad test procedure birthing pains. I found out I needed to let the gel blocks freely flop around instead of trying to restrain them. You might say I had to file down the corners of my test method wheel.

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“So, the Geezer is human after all,” thought Donny. He momentarily thought about scratching on that obvious scab, but decided he wanted no more intellectual birdshot aimed at his a$$.

D: So where did the solid copper bullets finish in your contest? I’m particularly interested in the 30-caliber, 165-grainer shot from the 308 Winchester.

GG: The ‘large’ tipped 225-grainer finished fifth behind the 30-caliber, 240-grainer cup and core, tipped match bullet. The ‘small’ tipped 225-grainer finished seventh, and the 165-grainer finished tenth. And if you can call it finishing, the stock, 35-caliber 225-grainer finished eleventh.

D: Last?

GG: Yep.

D: Why did the ‘small’ tipped, 35-caliber 225-grainer and the 30-caliber, 165-grainer finish so poorly?

GG: You tell me.

D: The wound cavity volumes were likely poor.

GG: Pretty much. The 7th place ‘small’ tipped 225-grainer had a wound cavity volume 46% greater than the 165-grainer, which is a good indicator of how poor the wound cavity volume was for the 165-grainer.

D: (Smirking again) Then answer me this. When I interviewed the PHs at the outdoor show in Harrisburg, one of them said the preferred chambering and ammo combination for taking a kudu was a 308 Winchester shooting a 165-grain, as you say, solid copper bullet. If you run game weight estimate numbers with your empiricism, it only comes out about 550 pounds at the muzzle. (Whereupon Donny produced his phone, drawn like a pistol.) You say your average shot distance is 135 yards and your test impact velocity was 2350 fps. That means (thumbs flying over the phone’s face) that bullet is only good for an animal weighing 480 pounds, not nearly enough for a trophy kudu bull. Explain that!

Donny felt he had snatched victory from the jaws of defeat. The Old Man had completely fallen into the numbers trap he had cleverly set. The irony was

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deliciously sweet; the Geezer would fall victim to his own empiricism and testing method mental masturbation.

GG grinned at the Pilgrim. Donny could see it was that damned Cheshire cat grin. He involuntarily braced.

GG: Fabulous question! The answer resides in PH operational issues.

Remember when we talked about the benefit of ‘perforate to ventilate’? The 165-grainer will damn well do it. Give a tracker even a small blood trail to follow, and the odds of losing an animal decrease significantly, maybe even close to zero. If you impact anywhere in the boiler room, you will get a blood trail.

These professional hunters encounter all manner of clients, some of whom couldn’t hit the side of a barn from 20 yards away. Recoil from uber magnums on folks that don’t take man pills and don’t practice off of sticks are likely primarily responsible. With a 308 Winchester, the recoil is relatively modest, likely enabling at least an impact on the lungs. If clients show up without a rifle for any reason, they are typically furnished this rifle-ammo combo to reduce the prospect of a poorly placed shot with the potentially bad outcome of an unrecovered animal.

Although meat damage is not a consideration for us, it is to them. The meat is sold for processing. The smaller wound cavity volume from this bullet translates into less blood-shot meat, and thus more profit, day in and day out.

As far as I’m concerned, any PH has the right to veto any numbers analysis I come up with. His experience, preferences, and choices govern. A PH gets the last word. Period. His reputation and multiple lives are at stake. Mine isn’t.

D: But what about your empiricism failing to predict the weight of a kudu bull that the PH says the 308 Winchester with a 165-grainer is good for?

GG: (Again, grinning like a Cheshire cat) I suppose that falls under the heading of ‘you can kill anything with anything’, particularly your 270 Winchester. ‘Kill’ is the operative word rather than ‘stop’. Even with a native African tracker, you may do more hunting after the shot than before it. Regardless, I believe the odds of a lost animal are increased by using this lighter weight bullet, cosmic tracker expertise notwithstanding.

“Damn him,” thought Donny.

D: (Still defiant) I know the manufacturer of that bullet ‘cause I looked it up. How come you never reference any manufacturers and specific bullets?

GG: Simple. Manufacturers’ reputations are at stake. I do not want to give the impression I am pointing fingers at specific manufacturers or awarding blue ribbons or boobie prizes for specific bullets, particularly because my testing methods and evaluation techniques are not mainstream, not even close. Plus, the testing sample population is so low.

The broader point is that I am trying to describe terminal performance that can be typically expected from each generic bullet design. The expected wound cavities and penetrations that are typically characteristic of these generic designs are a matter of hunter choice, with no set of performance characteristics being ‘best’. If folks want to get fixated on ‘best’ within a specific generic design, fine. I expect the terminal performance differences among different bullets within most generic designs would be relatively subtle compared to the terminal performance differences among the actual designs.

D: But what would you say to the chief engineer of this manufacturer if he were sitting here listening to all this? You have just said that two stock bullets that his company produced finished next to last and last in your competition.

GG: If he disagreed with any of this, I would invite him to show me his data and tell me how I am in error, based on those data. The primary metrics causing poor finishes of those bullets in my ranking are associated with wound cavity volume. I would love to know how he measures it, the magnitudes he gets, and what conclusions he draws.

The chief engineer may have concerns about how the rankings were actually determined. To be blunt, he would want to know if and how the deck was stacked against his solid copper bullet’s generic design. I would sketch out the conceptual cavity and show him the seven ways I measured it. Three are based on length; one is based on diameter; two are based on volume; and one is a calculation based on test data that I believe results in an indicator of how capable the bullet is at producing hydrodynamic shock. I would state that I decided upon these seven metrics based on my conceptual wound cavity before any actual tests were performed. I would show the simple math associated with the ranking scores. I would show him my data and tally sheets so he could see the test values with associated scores.

As I am reminding you, I would state that each generic bullet design has inherent benefits and limitations. Again, there is no ‘best’ bullet. Horses for courses based on an individual hunter’s performance preferences and his hunting problem definition. That is why I did this testing in the first place. I had a defined hunting problem that dictated the actual test distance. Based on that test distance and resultant impact velocities, I wanted to identify any generic bullet benefits or limitations based on wound cavity volume and penetration into a common testing medium. My testing, my measurements, my analysis, my choices of performance. I think all hunters should be given such data and allowed the opportunity to make their own choices for their horses on their courses.

Donny knew GG was right. His game, his rules, his scoring, his choices. And he also knew that the manufacturer of the solid copper bullets GG had tested offered no published terminal performance guidance or recommendations in the form that would satisfy the Old Man.

D: Would you expect different gel test results if you had tested a bullet from this manufacturer that had a factory-installed poly tip?

GG: More than likely. Different hole, maybe different annealing in the tip area, all potentially contributing to a somewhat increased wound cavity volume with a limited decrease in penetration length. If this manufacturer furnished comprehensive gel test results for all their bullets, no one would care about these ‘what-might-could-be’s’.

D: Have you made any conclusions concerning impact velocity ranges for this generic bullet?

GG: The manufacturers offer no published clues or guidance concerning a representative impact velocity range for this generic bullet. Based on my testing, I would say the impact velocity on the shoulder needs to be at least 2300 fps in order to be sure of getting an un-tipped solid copper bullet to expand. I have no idea what that impact velocity might be for a solid copper bullet with a factory-installed poly tip.

I have read accounts from media types and practitioners that are of the opinion that this lower-bound impact velocity is as low as 2100 fps to as high as 2600 fps. My impact velocity for the stock 225-grainer was 2220 fps in stout, 20%

synthetic gel. If weaker FBI ordinance gel were used, or the impact was in the lungs, it could very well be as high as 2600 fps.

D: No upper bound?

GG: As I have indicated, manufacturers are not really forthcoming. I can only speculate based on what occurred on a hunt the second time I went to Africa. I was hunting on property where an Australian hunter had not recovered a blue wildebeest he had shot with his 300 Winchester. My PH had been informed by the property owner to be on the lookout for it. While stalking my kudu, we encountered the wounded wildebeest. My PH used my 375 H&H and 300-grainer to drop it so it could be claimed.

I asked that the skinner save my bullet so I could see how it performed. I was presented with two bullets. One was obviously my 300-grainer. The other was just a 30-caliber solid copper cylinder. I later figured out that it was the remnants of what I believe was a 165-grain solid copper bullet that had all four mushroom petals sheared off from the impact stresses.

I don’t know anything about the hunt circumstances, such as the Australian hunter’s shot distance or where specifically on the wildebeest the bullet was recovered. Furthermore, the 300 Winchester the hunter used may not have had a stock chamber. All that being said, I would limit an impact velocity to 3100 fps for shot placement on the shoulder unless a manufacturer says otherwise.

Based on what we have discussed, what are your takeaways concerning a solid copper bullet’s terminal performance?

D: First and foremost, I conclude they are primarily designed to penetrate so there are no limitations on shot angle. The bullet’s tip is the focus of those design features where limiting the maximum extent to which the bullet mushrooms, controlling the rate of what expansion is allowed to occur, and keeping the resultant mushroom symmetric are all important in achieving that penetration performance.

GG: Excellent summation. What about impact velocity and its effect on performance of solid copper bullets?

D: In some ways, it’s kindly the opposite of cup and core bullets. Based on what you have told me, solid copper bullets likely have a sweet-spot range at

much higher velocities than cup and core bullets. Whereas there can be a significant drop-off in performance at high impact velocity with a cup and core bullet, the significant drop-off in performance for a solid copper bullet appears to occur at low impact velocities. But with both designs, there is an upper impact velocity that can cause these bullets to literally fail.

GG: Bingo. You can’t defy physics and strength of materials. There is no such thing as an ‘unlimited’ upper impact velocity.

Expansion at the expense of penetration or penetration at the expense of expansion was the performance extreme dichotomy I was trying to point out when I chose these two generic bullet designs to be discussed first. There are three other generic designs that I believe are capable of a balance between these performance characteristics in modern, high velocity chamberings within a relatively broad sweet-spot of impact velocities. At low impact velocities, they won’t expand very much, and at high impact velocities, they will fail. But in between these two qualitative impact velocity extremes, I believe they are capable of producing relatively consistent performance balanced between wound cavity volume and penetration.

D: Goldilocks bullets?

GG: You said it, not me.